White balance adjustment apparatus

Abstract: A white balance adjustment apparatus for adjusting red, green and blue video signals of an aiming subject has amplifiers (5a, 5b, 5c) for amplifying the R, G, B video signals, respectively, a brightness detector (7) for detecting the brightness of the subject, and a mode selector (8) for selecting either an outdoor lighting mode or an indoor lighting mode in accordance with the brightness detected by the brightness detector. A white detector (2) is provided for receiving the R, G, B video signals for each pixel and detecting a pixel with R, G, B video signals that falls in a narrow white range when the outdoor lighting mode is selected, and in a wide white range when the indoor lighting mode is selected. An integrator (3) integrates the number of detected pixels in the white range. A white balance gain control (4) controls the gain of the amplifiers based on the integrated result of the integrator.

Description: The present invention relates to a white balance adjustment apparatus as used in video cameras and similar devices. Such an apparatus comprises: amplifying means for amplifying said color component video signals separately; white detecting means receiving said color component video signals for each pixel; cumulating means for cumulating the number of detected pixels; and white balance gain calculation means for controlling the gain of said amplifying means based on the cumulated result of said cumulating means. As the performance of white balance adjustment apparatuses for video cameras has improved in recent years, internal metering devices requiring no external sensors have become the mainstream. White balance control is the process whereby the color temperature of the light source on the subject being imaged by the camera is detected and compensation is applied so that achromatic image areas are recorded achromatically, i.e., so that white is white. Examples of this type of white balance adjustment apparatus are described in JP-A- 61-184079 and EP-A- 530 738. An example of this conventional white balance adjustment apparatus is described below with reference to Figs. 4 and 5. Fig. 4 is a block diagram of a conventional white balance adjustment apparatus comprising input terminals 1, white detector 2, integrator 3, white balance gain calculator 4, amplifier 5, and output terminals 6. Fig. 5 is an example showing the white detection area of the white detector 2 in this conventional white balance adjustment apparatus. In Fig. 5, the axis of abscissas is the B/G axis, the axis of ordinates is the R/G axis, the dotted line is the axis of color temperature change, and the area contained within the solid line is the white detection area. The red (R), green (G), and blue (B) video signals input to input terminals 1a, 1b, and 1c are input to the white detector 2. The white detector 2 passes as output signals Rw, Gw, and Bw only those near-achromatic signal components of the input video signal that are within the white detection area shown in Fig. 5. The integrator 3 integrates one field of the near-achromatic video signal output from the white detector 2, and outputs integrated values Rs, Gs, and Bs. The white balance gain calculator 4 then calculates the white balance gain from the output signals Rs, Gs, and Bs from the integrator 3, and adjusts the amplification factor of the amplifier 5. The white-balanced video signals R', G', and B' are then output from the output terminals 6a, 6b, and 6c. Because the video signals entering the white detection area are not necessarily achromatic, when relatively pale colors near the axis of color temperature change, e.g., white skin tones and greenery outdoors, enter the screen, the conventional apparatus described above falsely determines these color signals to be achromatic, resulting in washed-out colors with white skin tones becoming white. Therefore, an object of the present invention is to provide a white balance adjustment apparatus for suppressing fading due to low saturation chromatic colors. To achieve this object, according to the present invention, a white balance adjustment apparatus for adjusting color component video signals video of an aimed subject, according to the preamble of claim 1 is characterized by brightness detecting means detecting the brightness of the subject; and mode selecting means for selecting either one of an outdoor lighting mode and an indoor lighting mode in accordance with the brightness detected by said brightness detecting means; said white detecting means detecting pixels of said color component video signals that falls in a narrow white range when said outdoor lighting mode is selected and in a wide white range when said indoor lighting mode is selected. The white balance adjustment apparatus thus sets a white detection area according to the subject brightness information detected by the brightness information detecting means, integrates only the signals entering the set white detection area, and calculates the white balance gain from the integrated values to adjust the amplification factor. It is therefore possible to restrict the white detection area to the outdoor light distribution area when operating under bright outdoor lighting, thereby preventing the false evaluation of chromatic signals as achromatic signals even when relatively light colors near the axis of color temperature change, such as white skin tones and outdoor greenery, enter the screen. The present invention will become more fully understood from the detailed description given below and the accompanying diagrams wherein: Fig. 1 is a block diagram of a white balance adjustment apparatus according to the first embodiment of the present invention; Fig. 2 is a block diagram of a white detector in the first embodiment; Fig. 3 is a graph of the color temperature coordinate space showing the white detection area of the white balance adjustment apparatus in the first embodiment of the invention; Fig. 4 is a block diagram of a conventional white balance adjustment apparatus; and Fig. 5 is a color temperature coordinate space graph showing the white detection area of the white detector in a conventional white balance adjustment apparatus. An embodiment of a white balance adjustment apparatus according to the invention is described below with reference to the accompanying figures. The object of this embodiment is to use brightness information to determine whether the subject being recorded is exposed under a strong light, such as outdoor light, or under weak light, such as indoor light, and to prevent color fading and similar operating errors by restricting the color temperature detection frame when operating under strong light as in outdoor light. Fig. 1. is a block diagram of a white balance adjustment apparatus according to the embodiment of the invention. As shown in Fig. 1, the white balance adjustment apparatus comprises input terminals 1a, 1b, 1c, a white detector 2, an integrator 3, a white balance gain calculator 4, amplifiers 5a, 5b, 5c, output terminals 6a, 6b, 6c, brightness detector 7, and mode selector 8. As shown in Fig. 2, the mode selector 8 comprises a comparator which determines whether the subject being currently recorded is illuminated by strong light (outdoor light) or weak light (indoor light) based on the output signal from the brightness detector 7, and outputs a HIGH signal if the primary light source is determined to be strong light (outdoor light); it otherwise outputs a LOW signal. The brightness detector 7 used here may be the adjustor for the iris mechanism that adjusts the exposure of the imaging device. The comparator in the mode selector 8 compares the iris adjustment signal with a predetermined threshold level Thf, and determines the primary light source to be strong outdoor light when the iris is closed beyond a certain level, that is when the iris adjustment signal is greater than the threshold level Thf, and thus produces a HIGH signal. The red (R), green (G), and blue (B) video signals input to input terminals 1a, 1b, and 1c, and the output signal from the mode selector 8 are then input to the white detector 2. Fig. 2 also shows a block diagram of the white detector 2 in a white balance adjustment apparatus according to the embodiment of the present invention. As shown in Fig. 2, the white detector 2 comprises amplifiers 9a, 9b, 9c, 9d, 9e, 9f, 9g, 9h, 9i, 9j, comparators 10a, 10a, 10c, 10d, 10e, 10f, 10g, 10h, adders 11a, 11b, AND circuits 12a, 12b, 12c, an OR circuit 13, and multiplexers 14a, 14b. The B signal input to input terminal ld of the white detector 2 is input to comparators 10a, 10b, and 10g. The B signal input to input terminal 1d is also doubled by amplifier 9a and added to the R signal by adder 11a, and the sum signal (R + 2B) is input to comparators 10c and 10d. The R signal input to input terminal 1e is doubled by amplifier 9b and added to the B signal by adder 11b, and the sum signal (2R + B) is input to comparators 10e, 10f, and 10h. The G signal input to input terminal 1f is multiplied α, β, δ, ε, ζ, η,  and times, respectively, by amplifiers 9c, 9d, 9e, 9f, 9g, 9h, 9i and 9j, and the resulting products are input to comparators 10a, 10b, 10g, 10c, 10d, 10e, 10f, and 10h, respectively. Comparator 10a compares the B signal with the α-times multiplied G signal, and outputs a HIGH signal if the B signal is greater. Comparator 10b compares the B signal with the β-times multiplied G signal, and outputs a HIGH signal if the β-times multiplied G signal is greater. Comparator 10c compares the (R + 2B) signal with the ε-times multiplied G signal, and outputs a HIGH signal if the (R + 2B) signal is greater. Comparator 10d compares the (R + 2B) signal with the ζ-times multiplied G signal, and outputs a HIGH signal if the ζ-times multiplied G signal is greater. Comparator 10e compares the (2R + B) signal with the η-times multiplied G signal, and outputs a HIGH signal if the (2R + B) signal is greater. Comparator 10f compares the (2R + B) signal with the -times multiplied G signal, and outputs a HIGH signal if the -times multiplied G signal is greater. Comparator 10g compares the B signal with the δ-times multiplied G signal, and outputs a HIGH signal if the B signal is greater. Comparator 10h compares the (2R + B) signal with the -times multiplied G signal, and outputs a HIGH signal if the (2R + B) signal is greater. AND circuit 12a outputs a HIGH signal when the outputs from comparators 10a, 10c, 10d, and 10e are all HIGH. AND circuit 12b outputs a HIGH signal when the outputs from comparators 10b, 10e, 10f, and 10g are all HIGH. AND circuit 12c outputs a HIGH signal when the outputs from comparators 10b, 10f, 10g, and 10h are all HIGH. The OR circuit 13 outputs a HIGH signal when the output from either AND circuit 12a or AND circuit 12b is HIGH. As a result, the OR circuit 13 outputs a HIGH signal when the condition defined by equation 1 below is satisfied. {αG < B < δG AND εG < (R + 2B) < ζG AND 2ηG < (2R + B)} or {δG < B < βG AND 2ηG < (2R + B) < 2G} The AND circuit 12c outputs a HIGH signal when the condition defined by equation 2 below is satisfied. The signal area or region satisfying these conditions is simulated in Fig. 3. In Fig. 3, the axis of abscissas is (B/G), the axis of ordinates is (R/G), and the dashed line in the shape of "<" is the axis of change in the color temperature of the light source. The wide region in which the OR circuit 13 outputs HIGH is the "<" shaped region defined by the solid line and indicated as a "first white detection area", and the narrow region in which the AND circuit 12c outputs HIGH is the shaded area which is indicated as a "second white detection area". The gain of amplifiers 9c - 9j is adjusted so that this "<" shaped wide region covers the spectrum of both outdoor light and artificial light ranging in color temperature from, for example, 3000-K halogen lamps to 10,000-K outdoor light, and the shaded narrow region covers the spectrum of only outdoor light ranging in color temperature from, for example, 4500-K to 10,000-K. In other words, a point is plotted in the graph of Fig. 3 in response to every pixel video data. The OR circuit 13 produces a HIGH signal when the plotted point falls within the first wide white detection area, and the AND circuit 12c produces a HIGH signal when the plotted point falls within the second narrow white detection area. Since the second narrow white detection area is completely contained in the first wide white detection area, the plotted point that falls in the second narrow white detection area always falls in the first wide white detection area. The first wide white detection area is defined as an area in which the pixel color can be considered as white under indoor (weak) lighting. The second narrow white detection area is defined as an area in which the pixel color can be considered as white under outdoor (strong) lighting. The output signals from the OR circuit 13 and AND circuit 12c are input to multiplexer 14a. When the white detection area setting signal from comparator 8 and input to input terminal 1g is LOW, representing the indoor weak lighting, multiplexer 14a selects the output signal from the OR circuit 13, as shown by the real line; and when the white detection area setting signal is HIGH, representing the outdoor strong lighting, multiplexer 14a selects the output signal from the AND circuit 12c, as shown by the dotted line. The B, R, and G signals input to the input terminals 1d, 1e, and 1f of the white detector 2, respectively, are also input to the second multiplexer 14b. When the output from the first multiplexer 14a is HIGH, the second multiplexer 14b is turned to a position shown by the real line, so that the video signals are selected and applied to terminals 6d, 6e and 6f; when the output of multiplexer 14a is LOW, the second multiplexer 14b is turned to a position shown by the dotted line, so that "0" (the ground level) is output. The output signals from the multiplexer 14b are thus output from output terminals 6d, 6e, and 6f as the achromatic video signals Bw, Rw, and Gw from the white detector 2. The Bw, Rw, and Gw output signals from the white detector 2 are then input to the integrator 3 for integrating each of the achromatic video signals Bw, Rw, and Gw. As shown in Fig. 2, the integrator for integrating the achromatic video signal Bw includes an adder and a delay. The adder adds the data cumulated in the delay. The delay is reset at the end of each field. Thus, the delay cumulates the achromatic video signal Bw from all the pixels that are detected as the white point pixels. The delay produces an integrated signal Bs. The integrators for integrating the achromatic video signals Rw and Gw have the same structure as the integrator for integrating the achromatic video signal Bw. Thus, after every field, integrated signals Rs, Gs, and Bs are output. Instead of the delay and adder, a counter can be used for cumulating the detected signal. The output signals Rs, Gs and Bs from the integrator 3 are input to the white balance gain calculator 4, which is defined by two dividers. The first divider divides the signal Gs by the signal Bs to produce a quotient signal Gs/Bs. Similarly, the second divider divides the signal Gs by the signal Rs to produce a quotient signal Gs/Rs. As shown in Fig. 1, the quotient signal Gs/Rs is applied to amplifier 5a which then produces a product signal R×(Gs/Rs). Similarly, the quotient signal Gs/Bs is applied to amplifier 5c which then produces a product signal B×(Gs/Bs). In this manner, the white-balanced signals are output from output terminals 6a, 6b, and 6c. If the second narrow white detection area is not provided as in the prior art, the spectral distribution of light yellow, light green, white skin-toned subjects under outdoor light will fall within the first wide white detection area, so that the light yellow, light green and white skin-toned subjects are forcibly made white or whitish in the reproduced image. However, according to the embodiment, since the second white detection area is provided for the outdoor lighting, the white balance gain control is done with respect to purer white colors, resulting in a high accuracy white balance. In the prior art, when the color temperature detection is done in the first white detection area in Fig. 3, the spectral distribution of yellow, green, and white skin-toned subjects under outdoor light will fall within this range, making light yellow and light green colors forcibly white. In other words, in the prior art, the white balance gain calculation is done for the whitish subjects that falls within the first white detection area for both indoor lights and outdoor lights. Thus, in the case of the outdoor lights, the light yellow, light green and white skin-toned subjects are all used for the basis of the white balance gain calculation. However, according to the embodiment, the white balance gain calculation is done with more whitish subject that falls in the second white detection area, so that white and other colors can be expressed with higher precision. The effect of the present invention thus described is to determine from the brightness information whether the primary light source is indoor weak light or outdoor strong light, and restrict the range of the white detection area when the primary light source is outdoor light. As a result, the effects of chromatic colors in the indoor light spectrum, e.g., yellows, green, and white skin tones, when exposed to outdoor light can be avoided to enable accurate white detection, and high precision white balancing can be obtained. It is to be noted that while an RGB primary color signal has been used by way of example in the description of the embodiment above, the same effects can be obtained using Y, R-Y, and B-y luminance and color difference signals by slightly modifying the configuration of the mode selector and the color temperature detector. Furthermore, the embodiment above applies a feed-forward type color temperature detection method using the signal before white balance adjustment, but the same effects can be obtained applying a feedback-type method using the signals after white balancing by slightly modifying the configuration of the mode selector and the color temperature detector. In addition, the video signal is used for color temperature detection in the embodiment above, but the same effects can be obtained by dividing each field into plural blocks and using the color signal representative of each block. Furthermore, when using representative color signals from plural signal blocks, all operations can be processed by a microprocessor in the embodiment above and the same effects can be obtained. In the above embodiment, red (R), green (G), and blue (B) video signals are used, but other color component signals, such as R-Y, B-Y and Y signals or magenta, green, cyan, and yellow signals can be used. When magenta, green, cyan, and yellow signals are used, the color temperature information Cbs and Crs will be used for the amplification factors of the amplifiers for the magenta+yellow and the magenta+cyan. By the invention thus described, it is possible to restrict the white detection area when exposed to particularly bright outdoor light by setting the white detection area according to the brightness information of the subject detected by a brightness detector, integrating only the signals within the set white detection area, calculating the white balance gain from the integrated values, and adjusting the amplification factor by the calculated white balance gain. As a result, even when relatively light colors, such as white skin tones and green outdoors, near the axis of color temperature change are in the field, the color signals therefrom will not be falsely detected as achromatic, and related operating errors, such as fading causing white skin tones to appear washed out, can be effectively prevented.

Claims: A white balance adjustment apparatus for adjusting color component video signals of an aimed subject, comprising: amplifying means (5a, 5b, 5c) for amplifying said color component video signals (R, G, B) separately; white detecting means (2) receiving said color component video signals (R, G, B) for each pixel; cumulating means (3) for cumulating the number of detected pixels; and white balance gain calculation means (4) for controlling the gain of said amplifying means (5a, 5c) based on the cumulated result of said cumulating means (3); characterized by brightness detecting means (7) detecting the brightness of the subject; and mode selecting means (8) for selecting either one of an outdoor lighting mode and an indoor lighting mode in accordance with the brightness detected by said brightness detecting means (7); said white detecting means (2) detecting pixels of said color component video signals that fall in a narrow white range when said outdoor lighting mode is selected, and in a wide white range when said indoor lighting mode is selected.

Inventors: MORI TSUTOMU, YAMAMOTO YASUTOSHI, YONEYAMA MASAYUKI, MORI, TSUTOMU, YAMAMOTO, YASUTOSHI, YONEYAMA, MASAYUKI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: H04N9
IPC codes: H04N9